From owner-freebsd-stable@FreeBSD.ORG Fri Feb 17 08:05:11 2012 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7C413106566B; Fri, 17 Feb 2012 08:05:11 +0000 (UTC) (envelope-from julian@freebsd.org) Received: from vps1.elischer.org (vps1.elischer.org [204.109.63.16]) by mx1.freebsd.org (Postfix) with ESMTP id 329F68FC0C; Fri, 17 Feb 2012 08:05:10 +0000 (UTC) Received: from julian-mac.elischer.org (c-67-180-24-15.hsd1.ca.comcast.net [67.180.24.15]) (authenticated bits=0) by vps1.elischer.org (8.14.4/8.14.4) with ESMTP id q1H858gq017634 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Fri, 17 Feb 2012 00:05:09 -0800 (PST) (envelope-from julian@freebsd.org) Message-ID: <4F3E0A90.6080400@freebsd.org> Date: Fri, 17 Feb 2012 00:06:40 -0800 From: Julian Elischer User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X 10.4; en-US; rv:1.9.2.26) Gecko/20120129 Thunderbird/3.1.18 MIME-Version: 1.0 To: davidxu@freebsd.org References: <4F3C2671.3090808__7697.00510795719$1329343207$gmane$org@freebsd.org> <4F3D3E2D.9090100@FreeBSD.org> <4F3D6FDD.9050808@freebsd.org> <4F3D89CD.9050309@freebsd.org> <4F3DA27A.3090903@freebsd.org> <4F3DB3DB.2060603@gmail.com> <4F3DB91A.2090806@freebsd.org> <4F3DBE90.5030305@gmail.com> <4F3E04AB.2000508@freebsd.org> In-Reply-To: <4F3E04AB.2000508@freebsd.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: David Xu , Alexander Kabaev , Andriy Gapon , threads@freebsd.org, FreeBSD Stable , Jung-uk Kim Subject: Re: pthread_cond_timedwait() broken in 9-stable? (from JAN 10) X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 17 Feb 2012 08:05:11 -0000 On 2/16/12 11:41 PM, Julian Elischer wrote: > adding jkim as he seems to be the last person working with TSC. > > > On 2/16/12 6:42 PM, David Xu wrote: >> On 2012/2/17 10:19, Julian Elischer wrote: >>> On 2/16/12 5:56 PM, David Xu wrote: >>>> On 2012/2/17 8:42, Julian Elischer wrote: >>>>> Adding David Xu for his thoughts since he reqrote the code in >>>>> quesiton in revision 213098 >>>>> >>>>> On 2/16/12 2:57 PM, Julian Elischer wrote: >>>>>> On 2/16/12 1:06 PM, Julian Elischer wrote: >>>>>>> On 2/16/12 9:34 AM, Andriy Gapon wrote: >>>>>>>> on 15/02/2012 23:41 Julian Elischer said the following: >>>>>>>>> The program fio (an IO test in ports) uses pthreads >>>>>>>>> >>>>>>>>> the following code (from fio-2.0.3, but its in earlier code >>>>>>>>> too) >>>>>>>>> has suddenly started misbehaving. >>>>>>>>> >>>>>>>>> clock_gettime(CLOCK_REALTIME,&t); >>>>>>>>> t.tv_sec += seconds + 10; >>>>>>>>> >>>>>>>>> pthread_mutex_lock(&mutex->lock); >>>>>>>>> >>>>>>>>> while (!mutex->value&& !ret) { >>>>>>>>> mutex->waiters++; >>>>>>>>> ret = >>>>>>>>> pthread_cond_timedwait(&mutex->cond,&mutex->lock,&t); >>>>>>>>> mutex->waiters--; >>>>>>>>> } >>>>>>>>> >>>>>>>>> if (!ret) { >>>>>>>>> mutex->value--; >>>>>>>>> pthread_mutex_unlock(&mutex->lock); >>>>>>>>> } >>>>>>>>> >>>>>>>>> >>>>>>>>> It turns out that 'ret' sometimes comes back instantly (on >>>>>>>>> my machine) with a >>>>>>>>> value of 60 (ETIMEDOUT) >>>>>>>>> despite the fact that we set the timeout 10 seconds into the >>>>>>>>> future. >>>>>>>>> >>>>>>>>> Has anyone else seen anything like this? >>>>>>>>> (and yes the condition variable attribute have been set to >>>>>>>>> use the REALTIME clock). >>>>>>>> But why? >>>>>>>> >>>>>>>> Just a hypothesis that maybe there is some issue with time >>>>>>>> keeping on that system. >>>>>>>> How would that code work out for you with MONOTONIC? >>>>>>> >>>>>>> Jens Axboe, (CC'd) tried both CLOCK_REALTIME and >>>>>>> CLOCK_MONOTONIC, and they both had the same problem.. >>>>>>> i.e. random early returns with ETIMEDOUT. >>>>>>> >>>>>>> I think we will try move out machine forward to a newer >>>>>>> -stable to see if it resolves. >>>>>> Kan upgraded the machine today to today's 9.x branch tip and >>>>>> the problem still occurs. >>>>>> 8.x does not have this problem. >>>>>> >>>>>> I have not got a 9-RELEASE machine to test on.. so I can not >>>>>> tell if this came in with the burst of stuff >>>>>> that came in after the 9.x branch was unfrozen after the >>>>>> release of 9.0. >>>>>> >>>>>> >>>>> >>>> I am trying to reproduce the problem, do you have complete >>>> sample code to test ? >>> >>> I'm still looking the exact set >>> but on my machine (4 cpus) the program from ports sysutils/fio >>> exhibits the problem when used with >>> kern.timecounter.hardware=TSC-low and with the following config file: >>> >>> pu05 # cat config.fio >>> >>> [global] >>> #clocksource=cpu >>> direct=1 >>> rw=randread >>> bs=4096 >>> fill_device=1 >>> numjobs=16 >>> iodepth=16 >>> #ioengine=posixaio >>> #ioengine=psync >>> ioengine=psync >>> group_reporting >>> norandommap >>> time_based >>> runtime=60000 >>> randrepeat=0 >>> >>> [file1] >>> filename=/dev/ada0 >>> >>> pu05 # >>> pu05 # fio config.fio >>> fio: this platform does not support process shared mutexes, >>> forcing use of threads. Use the 'thread' option to get rid of this >>> warning. >>> file1: (g=0): rw=randread, bs=4K-4K/4K-4K, ioengine=psync, iodepth=16 >>> ... >>> file1: (g=0): rw=randread, bs=4K-4K/4K-4K, ioengine=psync, iodepth=16 >>> fio 2.0.3 >>> Starting 15 threads and 1 process >>> fio: job startup hung? exiting. >>> fio: 5 jobs failed to start >>> Segmentation fault (core dumped) >>> pu05# >>> >>> >>> The reason 5 jobs failed to start is because the parent timed out >>> on them immediately. >>> It didn't time out on 10 of them apparently. >>> >>> >>> if I set the timer to ACPI-fast it works as expected.. >> maybe following code can check to see if TSC-LOW works by let the >> thread run >> on each cpu. >> >> gettimeofday(&prev, NULL); >> int cpu = 0; >> for (;;) { >> cpuset_t set; >> cpu = ++cpu % 4; >> CPU_ZERO(&set); >> CPU_SET(cpu, &set); >> pthread_setaffinity_np(pthread_self(), sizeof(set), &set); >> gettimeofday(&cur, NULL); >> if ( timercmp(&prev, &cur, >=)) { >> abort(); >> } >> } >> >> pu05# sysctl kern.timecounter.hardware=TSC-low kern.timecounter.hardware: ACPI-fast -> TSC-low pu05# ./test ^C pu05# cat test.c #include #include #include #include #include main() { int cpu = 0; struct timeval prev, cur; gettimeofday(&prev, NULL); for (;;) { cpuset_t set; cpu = ++cpu % 4; CPU_ZERO(&set); CPU_SET(cpu, &set); pthread_setaffinity_np(pthread_self(), sizeof(set), &set); gettimeofday(&cur, NULL); if ( timercmp(&prev, &cur, >)) { abort(); } prev = cur; } } pu05# ./test minutes pass....... ^C pu05# so it looks as if the TSC is working ok.. I'm just going to check that the program is actually moving CPU... yes it is moving around but I can't tell at what speed. (according to top). so we are still left with a question of "where is the problem?" kernel TSC driver? generic gettimeofday() code? pthreads cond code? the application?